This invention relates to a substrate support for a thermal processing chamber.
In many semiconductor device manufacturing processes, the required high levels of device performance, yield, and process repeatability can only be achieved if the temperature of the substrate (e.g., a semiconductor wafer) is tightly monitored and controlled during processing of the substrate.
Rapid thermal processing (RTP), for example, is used for several different fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN).
In some semiconductor processing systems, such as susceptorless systems, the substrate is supported around its perimeter with an edge ring. Some fabrication processes, such as RTCVD processes, can lead to the formation of deposits, such as silicon, on the edge ring as well as on the semiconductor substrate. Over time, the deposits accumulate on the edge ring. Moreover, due to variations in the placement of substrates within the edge ring pocket, the accumulated deposits may not be uniform across the surface of the substrate. Such uneven deposits may introduce undesired features on the backside of the substrate and adversely impact subsequent lithography or other processing steps, for example, if the substrates do not rest flat within the pocket of the edge ring. Therefore, the edge ring must be cleaned periodically so that the substrates rest properly on the edge ring and so that thermal interactions between the substrates and the edge ring do not adversely affect operation of the system.
One technique for cleaning the edge ring involves the use of a cleaning gas. To bring the edge ring to a temperature at which the cleaning gas is chemically effective, a surrogate substrate the same size as the semiconductor substrate can be used. During the cleaning process, the surrogate substrate is supported by the edge ring in the same manner as the semiconductor substrate. Such a cleaning procedure, however, can result in the surrogate substrate covering portions of the edge ring which have deposits thereon and which, therefore, should be cleaned prior to using the edge ring to process additional semiconductor substrates.